Elastic wave concentrator



Oct. 4, 1966 s. R. RICH ELASTIC WAVE CONCENTRATOR Filed June 16. 1965FIGS FIG.I

INVEN TOR STANLEY R. RICH ATTORNEYS United States Patent 3,276,419ELASTIC WAVE CON CENTRATOR Stanley R. Rich, West Hartford, Conn.,assignor to Teknika, Inc., Auburn, Mass., a corporation of DelawareFiled June 16, 1965, Ser. No. 464,273 6 Claims. (Cl. 116-137) Thisinvention relates to elastic wave generators and in particular to thehousing surrounding the wave generating element-s for directing andconcentrating the elastic wave energy.

Elastic wave energy generators are used increasingly today for defoamingand removing gases from liquid. One form of elastic wave energygenerator useful for this purpose is a whistle device in which gas underpressure is driven from a nozzle against a small resonant cavity toproduce sonic or ultrasonic waves. Elastic wave energy generators ofthis type are more fully described in US Patents 3,169,507 and3,169,509.

Elastic wave energy breaks foam bubbles by rapid compression anddecompression of the medium surrounding the bubble. As material formingthe bubbles becomes tougher and more resilient the elastic waveintensity must be increased to extremely high levels. The wavegenerators employ directive housings called herein concentrators forproviding a maximum intensity level in a localized volume. Even withconcentrators for focusing the wave energy, intensity drops withdistance so rapidly that where the wave generator is suspended in a tankit is necessary to place the wave generator in close proximity to thematerial being treated. The intensity of the elastic wave energy andother conditions are frequently such that the generator is exposed to acontinuous mist or spray derived from rupture of foam bubbles and/ ordisturbance of the gas/liquid interface of the material under treatment.

In the treatment of material that tends to aggl'omerate, film or congealreadily, the elastic wave generators used for defoaming and degasingfoul quickly due to the spray of substances from the material undertreatment. After some study it became apparent that generatorstructures, of the type disclosed in the above cited patents, produced agas flow pattern that contained a rarefied zone along the centnal axisof radiation. The rarefied zone attracts the spray of the material beingtreated so that it gradually works backward against the direction offlow of the exhaust driving fluid until the wave generating elements ofthe whistle become clogged. This is more fully explained in connectionwith FIG. 1 below.

In accordance with the present invention the applicant has found that bycurving in the outer rim of the concentrator, he can set up a cross fireof exhausted driving fluid that acts as a screen or curtain tending toprevent mist or spray developed from the treated material from enteringthe rarefied zone in the axial front of the generator. Thus it is anobject of the present invention to define concentrator means for anelastic wave generator.

It is a further object of the invention to define an antifoulingconcentrator for an elastic wave generator in a defoaming apparatus.

It is still a "further object of the present invention to define anelastic wave generator together with means to drive it in defoamingapparatus so that fouling of the generator is eliminated.

Further objects and features of the invention will be understood uponreading the following description together with drawings in which:

FIG. 1 is a cross-sectional view of a prior art device showing thecondition that produces fouling;

FIG. 2 is a similar cross-sectional view of an elastic wave generatorequipped with an antifouling concentrator in accordance with theinvention;

FIG. 3 is an exploded view of an elastic wave generator in accordancewith the invention; and

FIG. 4 is a cross-sectional view of a concentrator in accordance withthe invention.

FIG. 1 illustrates a prior art device which, when used to defoam orremove gas from liquids containing some types of coagulative or othergummy deposit forming material, fouls so as to be inoperative in a shorttime.

Exemplary liquids that cause this "fouling problem include manypaper-coating materials and polymer latices.

A feed pipe 10 introduces a drive fluid int-d the elastic wave generatorgenerally designated 11. This drive fiuid can be any fluid underpressure that is compatible with the particular use of the generator.That is the fluid should not contaminate or react undesirably with amaterial under treatment and should not create a hazardous condition,i.e. danger of fire or explosion. Air and/or steam are commonlypreferred fluids.

The drive fluid enters generator 11 through nozzle 12 facing resonantcavity 13. Needle point 15 protruding toward nozzle 12 from the centerof cavity 13 perturbs V the steam or drive fluid so that elastic wavesare set up at the resonant frequency of cavity 13.

Elastic waves and exhaust fluid pass out through radial channel 16defined by concave face 17 of cylindrical body 18 and by convex face 20of cylindrical body 21. Cylindrical body 21 is supported by standoffposts 22 to maintain the channel spacing between face 17 and face 20.

Cylindrical body 21 supports the cavity 13 and needle point 15arrangement as well as a hemispherical shaped dome 23 facing thedirection of energy propagation and serving to streamline the exteriorof the whistle elements improving acoustic efiiciency and reducingaccumulation of foreign matter. Concentrator 25 surrounds the abovedescribed generator elements and defines an enlarged annular passage fordirecting generated elastic wave energy in a concentrated path extendingin the axial line of the generator.

We are concerned here primarily with the passage and action of exhaustfluid leaving the generator. As is well known in fluid mechanics, afluid moving in a passage will tend to hug a sidewall of the passage.The inner wall of concentrator 25 and the surface of cylindrical body 21extending into the surface of hemispherical body 23 form such a passage.Exhaust fluid issuing from radial channel '16 preferentially hugs theinner wall of concentrator 25 as indicated by flow lines 26. The flowpattern formed by the exhaust fluid flowing outward from the wall ofconcentrator '25 produces relative rarefaction along the axis in frontof dome 23. This rarefaction results in an inward flow toward dome 23indicated by flow lines 27, This inward flow will normally include gasor mist ambient around the generator. Suspended liquid, or liquid thatcondenses on the surface of dome 23, creeps inward along the surface ofdome 23 eventually reaching channel 16. Finally, if the liquid containsdeposit-forming material, enough of this contamination collects torender the generator inoperative and it must be disassembled and cleanedbefore further operation.

An elastic wave generator similar to that of FIG. 1 but utilizing aconcentrator according to the present invention is illustrated in FIG.2. Similar elements in FIG. 2 are numbered as in FIG. 1. FIG. 2 shows aconcentrator 30 housing the wave generating elements of a generator 31otherwise essentially identical to generator 11. Concentrator 30comprises a first cylindrical section 32 which tits around cylindricalbody 18 and a second relatively enlarged cylindrical section 33 with awall spaced around the 'wave generating elements including hemisphericaldome 23. A first end of cylindrical section 32 is adapted to be aflixedto the inlet connection of generator 31. The second end of section 32and the first end of section 33 are joined by an outwardly curvingportion and the second or outlet end of section 33 terminates withinwardly curving lip 35.

As indicated by flow lines 36, exhaust fluid hugging the wall ofconcentrator 30 is directed inwardly by lip 35 so that fluid passingbeyond lip 35 takes the pattern of a hollow cone. The apex 3-7 of thiscone is located at some distance d (see FIG. 2) from the outlet end ofconcentrator 30 in the axial front of generator 31.

As in FIG. 1, the flow of the exhaust fluid moves outward from the wallof concentrator 30 leaving a relatively rarefied pressure zoneimmediately in front of dome 23. However, in generator 31 the inwardlycurving lip of concentrator 30 causes the flow to converge forward ofthe rarefied zone; This convergence of the flow limits access of ambientmists and gases to the region of relative rarefaction. Thus the rarefiedzone produces some recirculation of the exhaust fluid as illustrated inFIG. 2, with a greatly limited quantity of the mists and gases.

The driving fluid for the elastic wave generator 31 is supplied throughinlet pipe from pressurized sources 38 and 39. Valves '45, 4'6 and 47regulate fluid flow from sources 38, 39 and in pipe 10 respectively.Source 38 is a source of air or other nondiluent gas and source 39 is asource of diluent fluid such as water mist or steam. The term diluentdefines a material as having the quality to make thinner or more liquidby admixture. Diluent and nondiluent are used here in relation to thematerial the generator is intended to act on. For example, Water orsteam is a diluting agent with respect to a water suspension such as alatex.

It will be understood that generator fouling occurs when a material insuspension enters the wave generator and the .suspending liquidevaporates. This leaves residual solids deposited in the generator whichcan build up and render the generator inoperative. Thus a diluentmaterial as herein described would dilute the suspending liquid tomaintain the suspension and prevent depositing out of solids.

Sources 38 and 39 may be pressure tanks, pumps or other suitable meansof supplying gas or mist under pressure. For example source 39 may be asteam generator.

While air alone is suitable for some applications and for short runs, ithas been found preferable to add a fluid that will dilute substancesthat pass through the curtain of exhaust fluid. For example, in removingresidual monomer from a polymer latex, it has been found that watercontent in the exhaust fluid will dilute latex material that reaches thegenerator preventing it from drying so as to leave a deposit. While awater spray entrained with air for the drive fluid will serve thisfunction, steam has been found more desirable for most purposes.

Steam can be controlled to add adequate heat to compensate for thermalloss by adiabatic expansion. When Water is not a diluting agent for thematerial under treatment, some other diluent fluid that condenses at theexhaust end of the generator can be used.

It has been noted in monomer stripping that when some of the latex getsthrough and lands on hemispherical dome 2 3, that it immediately beginsto creep up into the generator. When steam is used as drive fluid, thelatex on dome 23 visibly dilutes to transparency, thins out andeventually is shaken from the dome surface out into the exhaust streamdue to the sonic vibration. With only air driving the generator, thedeposited latex dries and more is continually added to it in a gradualbuild up of latex on the generator elements.

, The radius of curvature of lip 35 determines the distance d in FIG. 2.In any particular utilization this distance must be less than thedistance x which is the distance between the lip of concentrator 30 andthe surface of liquid body 40 being acted on. When the generator ispositioned in a large chamber such as a centrifuge,

it has been found preferable to position the wave generator in closeproximity, i.e. 2 to 4 inches, to the liquid surface. Under theseconditions it has been found that a radius of curvature for lip 35 issuitably in the range of A to 1 inches in a concentrator of about 1%inside diameter.

The extent to which lip 35 extends inwardly to the axis of the generatoris limited by the need to maintain acoustical efficiency. Thus the totalcross-sectional area of the outlet opening should not be reduced fromthe cross-sectional area defined between hemispherical body 23 and thesidewall of section 33 of the concentrator. The reduction incross-section of body 23 toward the exhaust end of generator 31 permitssome inward curving of lip 35 without constriction in thecross-sectional area of the outlet passage.

The following chart illustrates the improved operation of the presentinvention for degasing and defoaming polyvinyl acetate latex at 40%solids. The transducer was positioned in a centrifuge 3 inches (distancex) from the vertical liquid surface. (Liquid surface vertical due tocentrifugal action.)

The curved-lip concentrator used above had a radius of curvature for thelip of about inch. The maximum inside diameter of the concentrator wasabout 1% inches and the inside diameter measured at the lip edges was 1inches.

FIG. 3 is an exploded view of generator 31 illustrated for a betterunderstanding of the assembly. A threaded section of inlet pipe 10together with the nozzle and radial channel assembly is generallydesignated assembly 42. Assembly 42 fits inside concentrator 30 which isfastened in place by nut 41 screwed down over pipe '10. Resonant chamberand needle assembly 43 fits into body 21 of assembly 42 andhemispherical dome 23 fits over resonant chamber and needle assembly 43.

FIG. 4 is a cross sectional view of novel concentrator 30 alone showingfirst cylindrical section 32, second enlarged cylindrical section 33 andinwardly curving lip 35.

While the invention has been described in relation to specificembodiments, it is intended that it be interpreted broadly within thespirit and scope of the appended claims.

What is claimed is:

1. A gas-driven elastic Wave energy transducer comprising means tointroduce gas under pressure, elastic wave generating means positionedin opposition to said means to introduce gas, a housing bisymmetricalabout a longitudinal axis, a first end of said housing closed about saidmeans to introduce gas, a second end of said housing open for radiationof Wave energy and disposal of exhausted gas, an inner wall of saidhousing surrounding said generating means and providing a continuouspath between said first end and said second end and a lip terminatingsaid second end, said housing particularly characterized in that saidlip curves inwardly so that a substantial portion of the gas exhaustfrom said transducer follows the inner wall of said housing and isdirected by said lip so that it crosses the longitudinal axis of saidhousing at a point spaced beyond said second end.

2. A housing according to claim 1 in which said lip is curved so as todirect said exhaust to converge at a point within three inches of saidopen end.

3. In an elastic wave transducer of the type in which a fluid streamunder pressure entering the transducer through an axial pipe isperturbed so that elastic waves are produced resonating at the frequencyof a cavity opposing the orifice of said pipe and then guided by aconcentrat-or designed to direct said elastic waves in a desiredpattern, the combination in said concentrator comprising a cylindricalhousing "having a first end fastened to said pipe, said housing bellingout in axial alignment with said pipe in the direction opposing saidorifice toward a second outer end of said housing and having an inwardlycurving lip at said outer end for directing the fluid exhaust issuingfrom said transducer along the inner Wall of said housing so that itangularly converges on the central axis of said housing at a pointspaced beyond said outer end.

4. An elastic wave transducer adapted to destroy foam and liberate gascomprising:

(a) means to introduce a fluid stream under pressure;

(b) means to perturb said stream so as to generate elastic waves;

(c) an orifice for the passage of said waves and the exhaust of saidstream from said transducer;

(d) means to guide said elastic waves and the exhaust of said fluidstream in a concentrated annular pattern between said means to perturband said orifice; and

(e) an inwardly curving lip terminating said means to guide at saidorifice for deflecting said exhaust of said fluid stream in an inwardlyconverging direction so as to form a curtain of exhaust fluid across thefront of said orifice, said curtain having the pattern of a hollow conewith its apex projected to a point along an extension of the transduceraxis in front of the transducer.

5. An elastic wave generator according to claim 4 in which said means toguide in a concentrated annular pattern comprises a concentratorsurrounding said transducer and a body positioned inside saidconcentrator in the central axis of said transducer terminating in arounded dome adjacent to said orifice and said means at said orifice fordeflecting is an inwardly curving lip of said concentrator which coactswith the rounding of said dome so as to maintain an undiminishedcross-sectional area between said means to perturb and said orifice.

6. An elastic wave generator adapted to destroy foam and liberate gasfrom a liquid body comprising:

(a) means to introduce a drive fluid containing a diluting agent forsaid liquid under pressure;

(b) means to perturb said fluid so as to generate elastic waves;

(c) an orifice for the passage of said waves and the exhaust of saidfluid from said generator;

(d) means to guide said elastic Waves and the exhaust of said fluid in aconcentrated annular pattern between said means to perturb and saidorifice; and

(e) an inwardly curving lip terminating said means to guide at saidorifice for deflecting said exhaust of said fluid in an inwardlyconverging direction so as to form a curtain of exhaust fluid across thefront of said orifice.

References Cited by the Examiner UNITED STATES PATENTS 1,727,861 9/1929Chapman 116-137 X 2,238,668 4/1941 Wellenstein 116-137 X 2,369,0202/1945 Clark 183-1 3,064,619 11/ 1962 Fortman 116-137 3,070,313 12/1962Fortman 116-137 3,107,647 10/1963 Soloff 116-137 3,118,748 1/1964Hans-Jurgen et a1. -292 3,169,509 2/1965 Rich 116-137 3,169,561 2/1965Berger et al. 141-69 3,182,710 5/1965 Mount 116-137 X LOUIS J. CAPOZI,Primary Examiner.

1. A GAS-DRIVEN ELASTIC WAVE ENERGY TRANSDUCER COMPRISING MEANS TOINTRODUCE GAS UNDER PRESSURE, ELASTIC WAVE GENERATING MEANS POSITIONEDIN OPPOSITION TO SAID MEANS TO INTRODUCE GAS, A HOUSING BISYMMETRICALABOUT A LONGITUDINAL AXIS, A FIRST END OF SAID HOUSING CLOSED ABOUT SAIDMEANS TO INTRODUCE GAS, A SECOND END OF SAID HOUSING OPEN FOR RADIATIONOF WAVE ENERGY AND DISPOSAL OF EXHAUSTED GAS, AN INNER WALL OF SAIDHOUSING SURROUNDING SAID GENERATING MEANS AND PROVIDING A CONTINUOUSPATH BETWEEN SAID FIRST END AND SAID SECOND END AND A LIP TERMINATINGSAID SECOND END, SAID HOUSING PARTICULARLY CHARACTERIZED IN THAT SAIDLIP CURVES INWARDLY SO THAT A SUBSTANTIAL PORTION OF THE GAS EXHAUSTFROM SAID TRANSDUCER FOLLOWS THE INNER WALL OF SAID HOUSING AND ISDIRECTED BY SAID LIP SO THAT IT CROSSES THE LONGITUDINAL AXIS OF SAIDHOUSING AT A POINT SPACED BEYOND SAID SECOND END.